The outcome will depend on several factors.
1) who has first strike and what type of strike it is
2) how effective the first strike is against the opponent
3) Thor's attitude - as he is always reluctant to fight women
4) Sersi's mindset i.e. relative calm or homicidal rage
Bear in mind that she has some awesome powers at her disposal
and has KO-ed Hercules with one punch when enraged.
Who you see as the winner of this battle depends on your personal
bias - the way that you choose to imagine the fight happening.